Hi Eric,

First, when you 'released' the door--were you able to bring it down gradually and with a 'light touch'? (It didn't crash to the ground, did it? If so, I'd definitely call in a professional.)

That said, I'm wondering if it might be possible to (with the chain off the sprocket) hit the button and have the opener 'finish' its cycle...then put things back together? BUT WHATEVER YOU DO---remember that a garage door can be VERY HEAVY (even 400 pounds) so take every precaution--keep kids and everyone else well away from the door while you're working anywhere near it!

But again, I'd wonder what maintenance has been missed to allow this problem to have happened in the first place. If the opener is having THIS problem, it's probably worth a safety checkup by a professional. Don't take safety lightly around a garage door....good luck.

You could remove the chain from the sprocket, raise the door one foot, let it sit on blocks while you reinstall the chain. Then it should be about right. Some additional adjustment will probably be necessary.
That said, I agree with the previous post that this door and opener need maintenance.
If you're handy, adjust the chain tension, lube the rollers and chain, and generally make sure it all works smoothly.
If you're uncomfortable with all that, call a pro.